A. Field of Invention
This invention relates generally to automotive braking systems and more specifically to the manufacture and use of automotive brake pistons.
B. Description of the Related Art
It is well known in the art to provide automotive vehicles with various types of brake systems. Some brake systems use a brake caliper mechanism that includes a pair of brake pads that straddle a brake rotor or disc and a brake piston that is positioned within a bore formed in the brake caliper housing. A drive mechanism is used to move the brake piston within the bore to force the brake pads into contact with opposite sides of the brake rotor to slow and stop the rotation of the brake rotor and thus to slow and stop the vehicle. One known drive mechanism uses hydraulic fluid pressure to cause the brake piston to move. Another known drive mechanism uses an electric motor to cause the brake piston to move. It is also known to combine a hydraulic brake system with an electric brake system to provide two methods for moving the brake piston. US Patent Application Publication No. 2007/0029142, for example, discloses a brake piston which can be moved with a hydraulic service brake operation and with an electric park brake operation.
It is known to form brake pistons out of steel due to the various forces and temperature variations exerted on them. Steel brake pistons offer advantages such as good chip resistance and good compression strength but they also come with disadvantages such as relatively large specific gravities and relatively high thermal conductivities. More recently, it is known to form brake pistons out of phenolic resin. Phenolic brake pistons offer advantages such as relatively low specific gravities and relatively low thermal conductivities but they also come with disadvantages such as poor chip resistance and a relatively low ash temperature.
Therefore, what is needed is a brake piston that combines the benefits of steel and phenolic resin.